WO2009135618A1 - Method and device for extracting water from humid ambient air - Google Patents

Abstract

The invention relates to a device and a method that permits the adsorption of the moisture present in the ambient air to a liquid adsorbent and the subsequent desorption of the diluted adsorbent in a desorber (9) in a manner supported largely by gravity. The need for auxiliary or externally supplied energy is therefore very low. The device operates largely with passive elements and is therefore easy to set up and very low-maintenance. The desorber (9) may, alternatively, be heated with solar energy, for example with the aid of a solar collector (36), with waste heat, or also with externally supplied energy.

Description

Title: Method and device for obtaining water from humid ambient air

description

In order to extract drinking water in arid or semi-arid areas, various technologies are known to extract water from the humidity contained in the ambient air.

Of the known technologies, namely cold condensation, capillary condensation, solids sorption and sorption with a liquid absorbent, the latter is the most promising.

An important advantage of sorbing with a liquid absorbent is that it is relatively easy and reliable to operate.

For reasons of linguistic simplification, the term "absorption" and "absorbent" will always be used in connection with the invention below. This always means an "adsorption" or an "adsorbent".

From DE 10 2004 026 334, to which reference is hereby made, a very advantageous device is known to absorb the water vapor contained in the ambient air in a liquid absorbent.

Absorption takes place by absorbing moisture from the liquid absorbent. In this case, the absorbent, usually a strongly saline solution, diluted. Since the water absorption takes place via the interface between the absorbent and the ambient air, a large interface is sought. The larger the interface, the more effective is the absorption of moisture in the air.

From the cited DE 10 2004 026 334 A1, substantially vertically aligned guide elements are provided for this purpose, which protrude upwards in the manner of a tower or are integrated in a tower-like construction. Above these guide elements, a storage for liquid absorbent is arranged. Absorbent is discharged from the reservoir in a controlled manner, so that the absorbent flows down on these guide elements driven by gravity. The absorbent absorbs moisture from the air and thereby thins.

Below the lower end of the guide elements, a collecting container is present, in which the diluted absorbent is collected.

It goes without saying that this absorption is particularly effective when the guide elements or the absorbent located on the guide elements is flowed around by the ambient air and thus takes place an intensive contact between the moist ambient air and the absorbent.

This first sub-process "absorption" of water extraction from the humidity can be carried out with the device described in DE 10 2004 026 334 Al in a very advantageous manner and at low cost.

The second sub-process "desorption" is to add the water contained in the diluted absorbent from the absorbent separate and thereby recover pure water. This separation is usually by evaporation.

Many technologies can be used for this evaporation. However, it is necessary for the successful use of a device for obtaining water from humid air in arid and semi-arid areas, that the apparatus design of such a desorption device, hereinafter referred to as "desorber", is low Desorber must also be robust and still require the least possible thermal or electrical energy.Preferably, a supply should be made from renewable energy sources.Only then are such systems for water production to operate economically and without large consumption of resources.

The invention has for its object to provide a method and apparatus for obtaining water from moist ambient air, which is preferably powered by renewable energy, in particular solar radiation and / or waste heat. Furthermore, the system should be simple in construction and operation, so it works reliably with low maintenance and low maintenance costs.

This object is achieved with the characterizing features of claim 1 and the independent device claim 4.

The features disclosed and claimed in the dependent subclaims describe advantageous embodiments of the method according to the invention and the device according to the invention.

Further advantages and advantageous embodiments are the following drawings, their description and the Claims removable. All of the features disclosed in the drawing, the description and the claims can be essential to the invention both individually and in any combination with one another.

In the drawing show:

Figure 1 shows the basic structure of an inventive

Device, Figure 2 shows an embodiment of an inventive

Device with single-stage evaporation, Figure 3 shows another embodiment of a device according to the invention with two-stage

Evaporation, Figure 4 shows another embodiment of a device according to the invention also with two-stage evaporation and Figure 5 a plurality of superimposed inventive

Device also with two-stage

Evaporation.

FIG. 1 schematically shows an absorber 1 known from DE 10 2004 026 334 A1. With regard to the operation of the absorber 1, reference is therefore made to this document.

A component of the absorber 1 is a storage 3 for the concentrated absorbent, which is arranged above a plurality of guide elements 5. In the embodiment shown in Figure 1, the guide elements 5 consist of a plurality of balls, which are strung on a steel cable or on a string. Now, when the concentrated absorbent from the memory 3 flows on the guide elements 5, the balls of the guide elements 5 ensure that increases the surface of the absorbent, the flow rate of the absorbent slowed down and thereby the absorption of the guide elements 5 umzufreichenden ambient air of water, from which the guide elements 5 umzufreichenden ambient air is improved.

Below the guide elements 5, a collecting container 7 is provided, in which the now diluted absorbent drops in from the guide elements 5.

In order for the absorbent to come into contact with the ambient air for as long as possible for a sufficiently long time, it is advantageous if the absorber 1 has a large dimension in the vertical direction. In particular, the length of the guide elements 5 in the vertical direction is an important parameter for influencing the performance of the absorber 1. Basically, the longer the guide elements 5 are, the larger the interface between the absorbent and the ambient air and the more moisture can be from the ambient air be recorded under otherwise identical conditions.

The second sub-process, namely the desorption, preferably takes place above the absorber 1, so that the desorber 9 is arranged at executed plants about 6 m to 12 m above the ground.

The Desorber 9 works with a vacuum evaporation. Thus, in the desorber 9 of the diluted absorbent from the container 7 again concentrated and the distillate, namely water, can be separated, the diluted absorbent is conveyed through a first line 11 from the collecting container 7 in the desorber 9. Because a negative pressure prevails in the desorber 9, the liquid absorbent is drawn in through the first line 11. Any required further feed pumps and shut-off valves are not shown. The desorber 9 is shown in Figure 1 only as a "black box". The operation of the desorber 9 will be explained in more detail with reference to the other figures.

It is important, however, that the Desorber 9 includes a vapor and airtight housing. In this case, the first line 11 opens. Furthermore, go from this housing from a second line 13, with the aid of which the concentrated absorbent is withdrawn from the desorber 9 and discharged into a collecting container 15.

A third line 17 starts from the desorber 9 and flows into a second collecting tank 19 for the distillate, namely the water obtained from the atmospheric moisture.

The water levels in the containers 15 and 19 are approximately at the same geodetic height and by an amount ΔH below the desorber 9. The geodetic height difference ΔH between the desorber 9 and the collection containers 15 and 19 may typically be 6 m to 10 m, so that due to the liquid column located in the lines 13 and 17 and the gravity acting on the liquid columns, a pressure in the housing of the desorber 9 of 0.4-0 bar absolute, corresponding to a negative pressure of 0.6 bar to almost 1 bar, sets.

Preferably, the liquid level is in the collection containers 15 and 19 below the collecting container 7. This makes it possible that in the desorption of the influx of concentrated absorbent 'is sucked through the first conduit 11 and then can flow into the lines 13 and 17.

Not shown in Figures 1 to 4, a vent valve, which at the top of the desorber. 9 is provided. In multi-stage desorbers, a bleed valve is provided for each stage. ^"About the vent valve of the desired suppressors can be set starting regular operation before. In addition, non-condensable gases can be removed from the desorber, if necessary. These gases are introduced with the liquid absorbent in the desorber. 9 Alternatively, it is also possible to Use vacuum pump.

Even from this description it is clear that both the generation according to the invention of a gravity-assisted vacuum in the desorber 9 and the absorber 1 require a certain height, so that a combination of these two sub-processes, an unillustrated frame "double" can be used, which In other words: the construction costs for a towering 6 to 10 m high stand are only incurred once and can be used profitably by both absorber 1 and desorber 9.

Furthermore, an optional feed line 21 and an optional return line 23 are connected to the desorber 9, which provide cooling water for a heat exchanger or condenser located in the desorber 9. A usually required circulation pump is not shown. As already shown in the schematic diagram of FIG. 1, most of the components of the device according to the invention are passive components. All that is needed is a pump 25 to convey the concentrated absorbent from the first sump 15 into the reservoir 3 and to overcome the geodetic difference in height between sump 15 and reservoir 3.

Furthermore, in some cases, a pump 27 is required to remove the diluted absorbent from the receiver 7 in the desorber 9 to promote. If possible, one tries to avoid the use of the pump 27. The

Drive power of these two pumps is relatively low. As a rule, due to the vacuum prevailing in the desorber 9, the diluted desorber is conveyed out of the collecting container 7 into the desorber 9 without the aid of the pump 27. In any case, the prevailing in the desorber vacuum 9 supports the pump 27, so that their power consumption is very low.

The flow line 21 and the return line 23 are optional.

FIG. 2 shows a further exemplary embodiment of a device according to the invention. In this embodiment, the lines 21 and 23 are not shown. Otherwise, the same components are provided with the same reference numerals and only the differences from FIG. 1 will be explained. Otherwise, what has been said with regard to FIG. 1 applies correspondingly.

In the embodiment of the desorber 9 shown in FIG. 2, a single-stage evaporation takes place.

The desorber 9 consists of an evaporator section 29 in which absorbent is present in liquid form. Above a liquid level, a steam atmosphere is present in the evaporator section 29 as well as in a distillate tank 31 of the desorber 9. The evaporator part 29 and the distillate container 31 are connected to one another via a connecting part 33 which lies above the liquid level in the evaporator part 29. Preferably, the connecting part 33 is inclined inclined relative to the horizontal in such a way that the connecting part 39 opens at a lower geodetic height in the distillate tank 31 as in the evaporator section 29th In the evaporator part 29, a first heat exchanger 35 is arranged, which is connected via tm2] lines, for example to a solar collector, a waste heat source and / or another heat source. Via this first heat exchanger 35, the absorbent located in the evaporator section 29 is heated until it has reached or exceeded a boiling point corresponding to the negative pressure prevailing in the desorber 9, so that the water contained in the liquid absorbent diluted by water evaporates.

In the connecting part 33, a second heat exchanger 37 or condenser is arranged, which is cooled by a cooling medium, such as water, so that condenses on its cold, in contact with the vapor located in the desorber condensed water vapor. It is also conceivable that the outer wall of the desorber 9 itself serves as a capacitor. Then, the condensate is formed on the inner surface of the distillate container 31.

Since the second heat exchanger 37 also for

Distillate container 31 is arranged sloping down, the distillate runs on the surface of the second heat exchanger in the direction of distillate tank 31 and drips, as soon as it has reached the lowermost end of the second heat exchanger 37, in the distillate tank 31. From the distillate tank 31, the distillate flows through the third Line 17 in the second collection container 19th

It is also possible to provide the container wall directly with air cooling, e.g. With a fan permanently dissipates heat through an air flow.

Solar thermal cooling units could still be mentioned, since they would have the advantage that you can use the solar panels required for the energy supply of Could use vacuum evaporation. Other options that can also be very advantageous depending on the location with photovoltaic operated refrigeration units or floor / air heat exchanger. At locations where there is a strong cooling of the air temperatures at night, the cold of the night can be stored for condensation on the day.

Furthermore, it is possible to use adsorption path for heat exchange. If the guide elements 5 of the absorption section are designed like a tube, the distillate produced in the desorber in the vacuum evaporation can be guided in the interior of the guide elements and thus be used to cool the absorbent flowing outside via the guide elements 5 and thereby achieve a higher water yield , As one skilled in the art knows, the hygroscopicity of many absorbents, such as a saline solution (eg, LiCl), decreases with increasing temperature as the vapor pressure difference between the solution and the ambient air decreases. Thus, it is more effective if the absorbent does not overheat. Experiments with LiCl have shown that the temperature should be kept below 40 ^° C., preferably even below 30 ^° C., in order to be able to ensure effective mass transfer of the water into the salt solution. The temperature of the distillate is in a temperature range of 15 ° C to 25 ° C move, so that a heat exchange is possible here.

The air flow through the absorption system can also be used to assist the condensation in the desorber 9 by heat is removed from the desorber 9. This brings another energetic advantage

As the absorbent is recirculated, the only source of contamination is the air itself. Particles, such as sand and dust, can be deposited continuously in a simple mechanical manner (eg, filters). With the right choice of the absorbent (eg salt and distilled water as the starting solution) is also avoided that deposits on the heat exchanger surfaces, which are primarily caused by calcium or magnesium compounds. The deposition problem: is a general problem in evaporator systems, the avoidance greatly increases the service life and process stability. Because of the mentioned geodetic height difference .DELTA.H between the distillate container 31 and the second reservoir 19 is formed in the third line 17 from a water column, which maintains the desired negative pressure in the desorber 9. The cooling of the second heat exchanger 37 can take place, for example, with the aid of the supply and return lines 21 and 23 shown in FIG.

As can be seen from FIG. 2, the device according to the invention is very simple and can be operated virtually maintenance-free. She works as follows:

With the aid of the first pump 25, concentrated absorbent is conveyed from the first collecting container 15 into the reservoir 3 of the absorber 1. From there, the absorbent slowly trickles down over the guide elements 5 and absorbs moisture from the air surrounding the guide elements 5. As a result, the absorbent dilutes and finally drips into the collecting container 7 below the guide elements 5.

From there, the now diluted absorbent passes via the first line 11 into the evaporator section 29 of the desorber. In the desorber 9 prevails, because of the water column present in the lines 13 and 17 and the geodetic height difference ΔH between the desorber 9 and the ends of the lines 13 and 17, a negative pressure, so that the Boiling point of the dissolved in the diluted absorbent water to, for example, 40 ⁰ C to 60 ⁰ C is lowered.

In the evaporator section 29 of the desorber 9 is a first heat exchanger, which is supplied for example via a solar collector 36 with solar generated heat. As a result, the liquid absorbent located in the evaporator part 29 heats up and the water dissolved in the liquid absorbent evaporates. This water vapor is condensed by means of the cooled by a cooling medium condenser 37 and deposited on the outer surface of the second heat exchanger 37. Thereafter, the distillate, namely water, drips into the distillate tank 31 and flows via the third line 19 into the second collecting tank 19 for the distillate.

It goes without saying that for the continuous operation of the system as well as for the start of the same still shut-off valves, such as valves, or pumps may be required, which are not shown here. Likewise, a control and various sensors are required, which are not shown here. These components can be installed as needed.

Of course, it is also possible to provide an electrically driven feed pump (not shown) between the solar collector 36 and the first heat exchanger 35. The same applies to the

Heat transfer circuit with which (not shown) of the second heat exchanger 37 is supplied with a cold heat transfer medium.

FIG. 3 shows a further embodiment of a desorber according to the invention, in which the desorber is designed in two stages [m4j.

In this two-stage desorber 9, there is a first evaporator section 29.1 and a first distillate tank 31.1 and a second evaporator section 29.2 and a second distillate tank 31.2.

The second evaporator part 29.2 is, for example, thermally conductively connected to the first distillate container 31.1 or to the connecting piece 33.1 [m5]. In the first stage of the desorber there is a slightly higher pressure than in the second stage of the desorber. This means that the boiling temperature of the absorbent present in the first evaporator part 29.1 is higher than that of the absorbent present in the second evaporator part 29.2.

If now the absorbent located in the first evaporator part 29.1 is heated with the aid of the first heat exchanger 35, the water contained in the absorbent evaporates and fills the entire space located above the liquid level. Since the second evaporator section 29.2 extends into the first distillate tank 31.1 and the boiling point of the absorbent located in the second evaporator section 29.2 is lower than the temperature of the steam present in the first distillate tank 31.1, the steam present in the first distillate tank 31.1 condenses on the outer surface of the second evaporator section 29.1 and is discharged via the line 17 into the second reservoir 19.

At the same time, the heat released during the condensation of the vapor condensed in the first distillate container 31 is used to heat the absorbent present in the second evaporator portion 29.2. This also evaporates the water contained in this absorbent, is condensed by means of the second heat exchanger 37 and then passes into the second distillate tank 31.2. From there, the distillate also passes through the third conduit 17 into the second collection container 19 for the distillate. It is of course possible and in many cases also useful to carry out a more than two-stage desorption. The number of stages within the desorber 9 ultimately depends on the external conditions and a profitability analysis. Thermodynamically, the highest possible number of stages is desirable, while for economic reasons, the number of stages is limited.

In the embodiment according to FIG. 3, the first line 11 opens into the second evaporator part 29.2. Between the second evaporator part 29.2 and the first evaporator part 29.1, a connecting line 39 is present. The removal of the concentrated by evaporation absorbent takes place from the first evaporator part 29.1 via the second line 13. This can be done for example by the difference in height in both containers. Alternatively, a small pump, not shown, can be used.

In the embodiment according to FIG. 4, the first evaporator part 29 and the second evaporator part 29. 2 are supplied directly with dilute absorbent via the first line 11. Likewise, the removal of the concentrated absorbent takes place directly and not via the second line 13. A connecting line between the first evaporator part 29.1 and the second evaporator part 29.2 is not present in this embodiment. There is also another option, namely to use a separate line for each stage to 17,11 and 13.

The advantage of the circuit variant according to FIG. 3 is the simpler structural design and the simpler piping. An advantage of the variant according to FIG. 4 is the simpler control of the removal of the concentrated absorbent. In addition, the concentration of the absorbent in the first evaporator section 29.1 and in the second evaporator section 29.2 are not coupled together. 5 shows the schematic structure of a "cascade" of a plurality of superimposed apparatus according to the invention for obtaining water, this construction with several modules, each comprising the sub-processes absorption and desorption, one above the other leads to further savings of pumps and containers, for example, concentrate discharge of a module in each case In order to move the absorbent and the distillate would thus be in the entire system only one pump needed, which greatly simplifies the overall structure and also other template, storage and intermediate container would be saved ,

The distillate could also be used to each support the condensation of the underlying Desorptionsmoduls 9 through a heat exchanger. For this, however, either different condensation temperatures in the individual desorption modules 9 would have to be realizable, or the distillate would have to be cooled further than necessary in order to allow condensation in the next module. Overall, then there is the advantage that the structure is further simplified, because not for each module own cooling unit and a cooling circuit must be provided.

Claims

claims 1. A process for the recovery of water from moist air, characterized by the following process steps Absorbing water from moist air in a liquid absorbent by the concentrated absorbent flowing downwards under the influence of gravity at one or more guide elements (5), Conveying the water-diluted absorbent into a desorber (9) with a gas- and vapor-tight sealable housing and with an evaporator section (29) and a distillate tank (31) for condensed water, Lowering the boiling point of the water dissolved in the absorbent by lowering the pressure in the desorber (9) Vaporizing the water dissolved in the absorbent by external heat input (35) Condensing the evaporated water at the surface of a second heat exchanger (37) and collecting the water dripping from the second heat exchanger (37). 2. The method according to claim 1, characterized in that the diluted absorbent is conveyed into the desorber (9), and that a mirror of the absorbent 'remains approximately constant in the evaporator. 3. A device for recovering water from moist air, with a recirculating liquid absorbent, wherein the absorbent alternately flows through an absorber (1) and a desorber (3), wherein the absorber (1) at least one extending in the vertical direction Guiding element (5), characterized in that the desorber (9) comprises an air and vapor-tight housing, that in the housing (9) at least one evaporator part (29), at least one distillate container (31) and a capacitor (37) in that means are provided for gravity-assisted generation of a negative pressure in the housing, and in that the desorber has a dilute absorbent feed line (11) and a condensed water outlet (17). 4. Apparatus according to claim 3, characterized in that the means for the gravity-assisted generation and / or maintenance of a negative pressure at least one partially filled with a liquid conduit (13, 17). 5. Apparatus according to claim 4, characterized in that the lines (13, 17) are filled with absorbent or water. 6. Device according to one of claims 3 to 6, characterized in that the desorber (9) at least one stage, preferably, multi-stage, is formed.